summaryrefslogtreecommitdiffstats
path: root/src/librustc_mir/transform/check_unsafety.rs
blob: 4081f827d4b3da98ba8acad19f731cee89375d40 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use rustc_data_structures::fx::FxHashSet;
use rustc_data_structures::indexed_vec::IndexVec;
use rustc_data_structures::sync::Lrc;

use rustc::ty::maps::Providers;
use rustc::ty::{self, TyCtxt};
use rustc::hir;
use rustc::hir::def_id::DefId;
use rustc::lint::builtin::{SAFE_EXTERN_STATICS, SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
use rustc::mir::*;
use rustc::mir::visit::{PlaceContext, Visitor};

use syntax::ast;
use syntax::symbol::Symbol;

use util;

pub struct UnsafetyChecker<'a, 'tcx: 'a> {
    mir: &'a Mir<'tcx>,
    visibility_scope_info: &'a IndexVec<VisibilityScope, VisibilityScopeInfo>,
    violations: Vec<UnsafetyViolation>,
    source_info: SourceInfo,
    tcx: TyCtxt<'a, 'tcx, 'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    used_unsafe: FxHashSet<ast::NodeId>,
    inherited_blocks: Vec<(ast::NodeId, bool)>,
}

impl<'a, 'gcx, 'tcx> UnsafetyChecker<'a, 'tcx> {
    fn new(mir: &'a Mir<'tcx>,
           visibility_scope_info: &'a IndexVec<VisibilityScope, VisibilityScopeInfo>,
           tcx: TyCtxt<'a, 'tcx, 'tcx>,
           param_env: ty::ParamEnv<'tcx>) -> Self {
        Self {
            mir,
            visibility_scope_info,
            violations: vec![],
            source_info: SourceInfo {
                span: mir.span,
                scope: ARGUMENT_VISIBILITY_SCOPE
            },
            tcx,
            param_env,
            used_unsafe: FxHashSet(),
            inherited_blocks: vec![],
        }
    }
}

impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
    fn visit_terminator(&mut self,
                        block: BasicBlock,
                        terminator: &Terminator<'tcx>,
                        location: Location)
    {
        self.source_info = terminator.source_info;
        match terminator.kind {
            TerminatorKind::Goto { .. } |
            TerminatorKind::SwitchInt { .. } |
            TerminatorKind::Drop { .. } |
            TerminatorKind::Yield { .. } |
            TerminatorKind::Assert { .. } |
            TerminatorKind::DropAndReplace { .. } |
            TerminatorKind::GeneratorDrop |
            TerminatorKind::Resume |
            TerminatorKind::Abort |
            TerminatorKind::Return |
            TerminatorKind::Unreachable |
            TerminatorKind::FalseEdges { .. } |
            TerminatorKind::FalseUnwind { .. } => {
                // safe (at least as emitted during MIR construction)
            }

            TerminatorKind::Call { ref func, .. } => {
                let func_ty = func.ty(self.mir, self.tcx);
                let sig = func_ty.fn_sig(self.tcx);
                if let hir::Unsafety::Unsafe = sig.unsafety() {
                    self.require_unsafe("call to unsafe function")
                }
            }
        }
        self.super_terminator(block, terminator, location);
    }

    fn visit_statement(&mut self,
                       block: BasicBlock,
                       statement: &Statement<'tcx>,
                       location: Location)
    {
        self.source_info = statement.source_info;
        match statement.kind {
            StatementKind::Assign(..) |
            StatementKind::ReadForMatch(..) |
            StatementKind::SetDiscriminant { .. } |
            StatementKind::StorageLive(..) |
            StatementKind::StorageDead(..) |
            StatementKind::EndRegion(..) |
            StatementKind::Validate(..) |
            StatementKind::UserAssertTy(..) |
            StatementKind::Nop => {
                // safe (at least as emitted during MIR construction)
            }

            StatementKind::InlineAsm { .. } => {
                self.require_unsafe("use of inline assembly")
            },
        }
        self.super_statement(block, statement, location);
    }

    fn visit_rvalue(&mut self,
                    rvalue: &Rvalue<'tcx>,
                    location: Location)
    {
        if let &Rvalue::Aggregate(box ref aggregate, _) = rvalue {
            match aggregate {
                &AggregateKind::Array(..) |
                &AggregateKind::Tuple |
                &AggregateKind::Adt(..) => {}
                &AggregateKind::Closure(def_id, _) |
                &AggregateKind::Generator(def_id, _, _) => {
                    let UnsafetyCheckResult {
                        violations, unsafe_blocks
                    } = self.tcx.unsafety_check_result(def_id);
                    self.register_violations(&violations, &unsafe_blocks);
                }
            }
        }
        self.super_rvalue(rvalue, location);
    }

    fn visit_place(&mut self,
                    place: &Place<'tcx>,
                    context: PlaceContext<'tcx>,
                    location: Location) {
        if let PlaceContext::Borrow { .. } = context {
            if util::is_disaligned(self.tcx, self.mir, self.param_env, place) {
                let source_info = self.source_info;
                let lint_root =
                    self.visibility_scope_info[source_info.scope].lint_root;
                self.register_violations(&[UnsafetyViolation {
                    source_info,
                    description: Symbol::intern("borrow of packed field").as_interned_str(),
                    kind: UnsafetyViolationKind::BorrowPacked(lint_root)
                }], &[]);
            }
        }

        match place {
            &Place::Projection(box Projection {
                ref base, ref elem
            }) => {
                let old_source_info = self.source_info;
                if let &Place::Local(local) = base {
                    if self.mir.local_decls[local].internal {
                        // Internal locals are used in the `move_val_init` desugaring.
                        // We want to check unsafety against the source info of the
                        // desugaring, rather than the source info of the RHS.
                        self.source_info = self.mir.local_decls[local].source_info;
                    }
                }
                let base_ty = base.ty(self.mir, self.tcx).to_ty(self.tcx);
                match base_ty.sty {
                    ty::TyRawPtr(..) => {
                        self.require_unsafe("dereference of raw pointer")
                    }
                    ty::TyAdt(adt, _) => {
                        if adt.is_union() {
                            if context == PlaceContext::Store ||
                                context == PlaceContext::AsmOutput ||
                                context == PlaceContext::Drop
                            {
                                let elem_ty = match elem {
                                    &ProjectionElem::Field(_, ty) => ty,
                                    _ => span_bug!(
                                        self.source_info.span,
                                        "non-field projection {:?} from union?",
                                        place)
                                };
                                if elem_ty.moves_by_default(self.tcx, self.param_env,
                                                            self.source_info.span) {
                                    self.require_unsafe(
                                        "assignment to non-`Copy` union field")
                                } else {
                                    // write to non-move union, safe
                                }
                            } else {
                                self.require_unsafe("access to union field")
                            }
                        }
                    }
                    _ => {}
                }
                self.source_info = old_source_info;
            }
            &Place::Local(..) => {
                // locals are safe
            }
            &Place::Static(box Static { def_id, ty: _ }) => {
                if self.tcx.is_static(def_id) == Some(hir::Mutability::MutMutable) {
                    self.require_unsafe("use of mutable static");
                } else if self.tcx.is_foreign_item(def_id) {
                    let source_info = self.source_info;
                    let lint_root =
                        self.visibility_scope_info[source_info.scope].lint_root;
                    self.register_violations(&[UnsafetyViolation {
                        source_info,
                        description: Symbol::intern("use of extern static").as_interned_str(),
                        kind: UnsafetyViolationKind::ExternStatic(lint_root)
                    }], &[]);
                }
            }
        };
        self.super_place(place, context, location);
    }
}

impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
    fn require_unsafe(&mut self,
                      description: &'static str)
    {
        let source_info = self.source_info;
        self.register_violations(&[UnsafetyViolation {
            source_info,
            description: Symbol::intern(description).as_interned_str(),
            kind: UnsafetyViolationKind::General,
        }], &[]);
    }

    fn register_violations(&mut self,
                           violations: &[UnsafetyViolation],
                           unsafe_blocks: &[(ast::NodeId, bool)]) {
        let within_unsafe = match self.visibility_scope_info[self.source_info.scope].safety {
            Safety::Safe => {
                for violation in violations {
                    if !self.violations.contains(violation) {
                        self.violations.push(violation.clone())
                    }
                }

                false
            }
            Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
            Safety::ExplicitUnsafe(node_id) => {
                if !violations.is_empty() {
                    self.used_unsafe.insert(node_id);
                }
                true
            }
        };
        self.inherited_blocks.extend(unsafe_blocks.iter().map(|&(node_id, is_used)| {
            (node_id, is_used && !within_unsafe)
        }));
    }
}

pub(crate) fn provide(providers: &mut Providers) {
    *providers = Providers {
        unsafety_check_result,
        unsafe_derive_on_repr_packed,
        ..*providers
    };
}

struct UnusedUnsafeVisitor<'a> {
    used_unsafe: &'a FxHashSet<ast::NodeId>,
    unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>,
}

impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
    fn nested_visit_map<'this>(&'this mut self) ->
        hir::intravisit::NestedVisitorMap<'this, 'tcx>
    {
        hir::intravisit::NestedVisitorMap::None
    }

    fn visit_block(&mut self, block: &'tcx hir::Block) {
        hir::intravisit::walk_block(self, block);

        if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
            self.unsafe_blocks.push((block.id, self.used_unsafe.contains(&block.id)));
        }
    }
}

fn check_unused_unsafe<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                 def_id: DefId,
                                 used_unsafe: &FxHashSet<ast::NodeId>,
                                 unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>)
{
    let body_id =
        tcx.hir.as_local_node_id(def_id).and_then(|node_id| {
            tcx.hir.maybe_body_owned_by(node_id)
        });

    let body_id = match body_id {
        Some(body) => body,
        None => {
            debug!("check_unused_unsafe({:?}) - no body found", def_id);
            return
        }
    };
    let body = tcx.hir.body(body_id);
    debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})",
           def_id, body, used_unsafe);

    let mut visitor =  UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
    hir::intravisit::Visitor::visit_body(&mut visitor, body);
}

fn unsafety_check_result<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
                                   -> UnsafetyCheckResult
{
    debug!("unsafety_violations({:?})", def_id);

    // NB: this borrow is valid because all the consumers of
    // `mir_built` force this.
    let mir = &tcx.mir_built(def_id).borrow();

    let visibility_scope_info = match mir.visibility_scope_info {
        ClearCrossCrate::Set(ref data) => data,
        ClearCrossCrate::Clear => {
            debug!("unsafety_violations: {:?} - remote, skipping", def_id);
            return UnsafetyCheckResult {
                violations: Lrc::new([]),
                unsafe_blocks: Lrc::new([])
            }
        }
    };

    let param_env = tcx.param_env(def_id);
    let mut checker = UnsafetyChecker::new(
        mir, visibility_scope_info, tcx, param_env);
    checker.visit_mir(mir);

    check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
    UnsafetyCheckResult {
        violations: checker.violations.into(),
        unsafe_blocks: checker.inherited_blocks.into()
    }
}

fn unsafe_derive_on_repr_packed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
    let lint_node_id = match tcx.hir.as_local_node_id(def_id) {
        Some(node_id) => node_id,
        None => bug!("checking unsafety for non-local def id {:?}", def_id)
    };

    // FIXME: when we make this a hard error, this should have its
    // own error code.
    let message = if tcx.generics_of(def_id).own_counts().types != 0 {
        format!("#[derive] can't be used on a #[repr(packed)] struct with \
                 type parameters (error E0133)")
    } else {
        format!("#[derive] can't be used on a non-Copy #[repr(packed)] struct \
                 (error E0133)")
    };
    tcx.lint_node(SAFE_PACKED_BORROWS,
                  lint_node_id,
                  tcx.def_span(def_id),
                  &message);
}

/// Return the NodeId for an enclosing scope that is also `unsafe`
fn is_enclosed(tcx: TyCtxt,
               used_unsafe: &FxHashSet<ast::NodeId>,
               id: ast::NodeId) -> Option<(String, ast::NodeId)> {
    let parent_id = tcx.hir.get_parent_node(id);
    if parent_id != id {
        if used_unsafe.contains(&parent_id) {
            Some(("block".to_string(), parent_id))
        } else if let Some(hir::map::NodeItem(&hir::Item {
            node: hir::ItemFn(_, fn_unsafety, _, _, _, _),
            ..
        })) = tcx.hir.find(parent_id) {
            match fn_unsafety {
                hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
                hir::Unsafety::Normal => None,
            }
        } else {
            is_enclosed(tcx, used_unsafe, parent_id)
        }
    } else {
        None
    }
}

fn report_unused_unsafe(tcx: TyCtxt, used_unsafe: &FxHashSet<ast::NodeId>, id: ast::NodeId) {
    let span = tcx.sess.codemap().def_span(tcx.hir.span(id));
    let msg = "unnecessary `unsafe` block";
    let mut db = tcx.struct_span_lint_node(UNUSED_UNSAFE, id, span, msg);
    db.span_label(span, msg);
    if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
        db.span_label(tcx.sess.codemap().def_span(tcx.hir.span(id)),
                      format!("because it's nested under this `unsafe` {}", kind));
    }
    db.emit();
}

fn builtin_derive_def_id<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Option<DefId> {
    debug!("builtin_derive_def_id({:?})", def_id);
    if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
        if tcx.has_attr(impl_def_id, "automatically_derived") {
            debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
            Some(impl_def_id)
        } else {
            debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
            None
        }
    } else {
        debug!("builtin_derive_def_id({:?}) - not a method", def_id);
        None
    }
}

pub fn check_unsafety<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
    debug!("check_unsafety({:?})", def_id);

    // closures are handled by their parent fn.
    if tcx.is_closure(def_id) {
        return;
    }

    let UnsafetyCheckResult {
        violations,
        unsafe_blocks
    } = tcx.unsafety_check_result(def_id);

    for &UnsafetyViolation {
        source_info, description, kind
    } in violations.iter() {
        // Report an error.
        match kind {
            UnsafetyViolationKind::General => {
                struct_span_err!(
                    tcx.sess, source_info.span, E0133,
                    "{} requires unsafe function or block", description)
                    .span_label(source_info.span, &description.as_str()[..])
                    .emit();
            }
            UnsafetyViolationKind::ExternStatic(lint_node_id) => {
                tcx.lint_node(SAFE_EXTERN_STATICS,
                              lint_node_id,
                              source_info.span,
                              &format!("{} requires unsafe function or \
                                        block (error E0133)", &description.as_str()[..]));
            }
            UnsafetyViolationKind::BorrowPacked(lint_node_id) => {
                if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
                    tcx.unsafe_derive_on_repr_packed(impl_def_id);
                } else {
                    tcx.lint_node(SAFE_PACKED_BORROWS,
                                  lint_node_id,
                                  source_info.span,
                                  &format!("{} requires unsafe function or \
                                            block (error E0133)", &description.as_str()[..]));
                }
            }
        }
    }

    let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
    unsafe_blocks.sort();
    let used_unsafe: FxHashSet<_> = unsafe_blocks.iter()
        .flat_map(|&&(id, used)| if used { Some(id) } else { None })
        .collect();
    for &(block_id, is_used) in unsafe_blocks {
        if !is_used {
            report_unused_unsafe(tcx, &used_unsafe, block_id);
        }
    }
}